Technical Field
The present disclosure relates generally to the field of combustion furnaces and methods of use, and more specifically to processes for producing molten glasses from glass batches using turbulent submerged combustion melting, and systems for carrying out such processes.
Background Art
In submerged combustion melting of glass and similar materials, combustion gases emitted from sidewall-mounted and/or floor-mounted burners are injected beneath the surface of a molten or partially molten mass of material being melted in a melter vessel and rise upward through the molten or partially molten mass. The molten or partially molten mass of material is a complex mixture of molten feed material (feed material is commonly referred to as “batch” in the glass industry), unmelted batch, and gases from the burners and evolved gases from the reaction of and/or decomposition of batch materials. Recycled glass or “cullet”, as well as various waste materials of varying glass content (such as fiberglass batting or even loose fibers) may also be present. The materials are heated at a high efficiency via the intimate contact with the combustion gases. Using submerged combustion burners produces violent turbulence of the molten material or partially molten material. Vibration of the burners and/or the melter vessel walls themselves, due to sloshing of molten material, pulsing of combustion burners, popping of large bubbles above or aside of submerged burners, ejection of molten material from the melt against the walls and ceiling of melter vessel, and the like, are possible.
Feeding batch to a turbulent submerged combustion melter often presents challenges. Fast melting is of course desired, and attempts have been made to achieve that goal in non-submerged combustion melters, such as changing the shape of the batch itself, or by compressing the batch blanket formed inside the melter, but these techniques affect the throughput of the melter (see for example the discussion in U.S. Pat. No. 4,004,903). Different mechanical devices, such as vacuum and rotary devices, have been proposed to remove air from batch for the purposes of increasing the melting rate of batch in non-submerged, non-turbulent combustion melters (see for example U.S. Pat. No. 3,325,298). None of the previous solutions have recognized, or had to deal with a particular problem associated with submerged combustion, that is the entrainment of a portion of the batch out of the melter before it even has a chance to melt. This can lead to off specification molten glass, and/or molten glass of inconsistent chemistry leaving the submerged combustion melter. Given that loss of batch out of a submerged combustion melter stack is unacceptable, reduction of batch loss would be welcome.
In contrast to the present disclosure, Rue, “Energy-Efficient Glass Melting—The Next Generation Melter”, Gas Technology Institute, Project No. 20621 Final Report (2008) advised that, in submerged combustion melters, batch handling systems can be simple and inexpensive because the melter is tolerant of a wide range of batch and cullet size and does not require perfect feed blending. The report also maintains that the size, physical nature, and homogeneity of the batch do not require strict control. While these statements may be true in the context of comparing submerged combustion to non-submerged combustion melting of glass batch, the inventors herein have discovered that, without particular attention to the physical condition of glass batch, loss of batch may be a significant problem in submerged combustion processes and systems.
It would be a significant advance in the glass melting art to develop processes of operating submerged combustion melters, and systems to carry out the processes in producing molten glass wherein the problem of batch loss is reduced or eliminated.